DE19648471A1 - Semiconductor nitride layer etching system - Google Patents

Abstract

Semiconductor nitride layer etching system comprises a device(1) for adding ammonium fluoride or buffered hydrofluoric acid to a chemical solution containing hot phosphoric acid solution.

Description

The invention relates to a semiconductor nitride layer etching system to stabilize the nitride layer etching rate of a semi-lead terwafers and the etch selectivity ratio.

Semiconductor nitride layers with different properties can be formed today with different methods and therefore there are more and more applications in semiconductors production. With increasing degree of integration of a semi-lead terbauelements the structure of the component is compli graced, and the types of coexisting layer ten depend on the process in which the layers be applied.

In general, wet has been used in nitride layer etching treatment and a treatment solution, the hot phosphorus contains acid, applied. With increasing degree of integration of a component and the complexity of the structure The device uses nitride layers and oxide nitride  layers with different properties are used. It is therefore difficult these layers of the nitride layer system using conventional treatment with hot phosphorus etching acid with high controllability.

Because the cross-sectional shape and purity of an integrated Circuit after etching are very important, it is at very important to a semiconductor manufacturing process that Etching selectivity ratio between a Ni to be etched tridschicht and other coexisting layers to control (e.g. SiOxNy-based layer: Ox, y2). The Etching selectivity ratio is determined by an equilibrium determined reaction, which is related to the etching, and thus serve an etchant, a reaction product and the tempera structure as a parameter of the reaction rate of the equilibrium reaction tion. Therefore, it is un to realize precise etching conditionally necessary to control these parameters.

Fig. 21 shows the configuration of a conventional circulation type nitride film etching system. The conventional etching system is designed so that the treatment solution is circulated through a treatment tank 1 , while the solution is simultaneously passed by a pump 2 through a filter 3 and heated by a heating device 4 and demineralized water is supplied by a drip device for demineralized water. This type of etching system is designed to control the concentration and temperature of only the phosphoric acid in the treatment solution, but it cannot control other components of the treatment solution. It is therefore difficult to optimally and stably maintain the etching rates of a nitride layer and other layers and the selectivity ratio between the nitride layer and other layers.

The invention serves to solve the above problems; The object of the invention is to provide a half lead ternitride layer etching system, the performance  the treatment solution is improved and the etching rate one Semiconductor nitride layer and the etching selectivity ratio be stabilized.

According to one aspect of the invention, a semiconductor nitride Layer etching system indicated, which is characterized by a device for adding ammonium fluoride or ge buffered hydrofluoric acid to a treatment solution, which contains essentially hot phosphoric acid.

According to another aspect of the invention is a semi-lead ternitride layer etching system, characterized in that a Device for detecting the fluorine concentration in the Treatment solution is provided to reduce the fluorine concentration by controlling the amount of fluorine to be added.

In another aspect of the invention is the semiconductor Nitride layer etching system characterized in that the Fluorine concentration in the treatment solution to 200 ppm or is less controllable.

According to another aspect of the invention, a semiconductor nitride layer etching system provided, which is marked is through a device for adding silicon or a silicon compound to the treatment solution, the mainly contains phosphoric acid.

In another aspect of the invention is the semiconductor nitride layer etching system characterized by a device device for detecting the silicon concentration in the loading solution, so that the silicon concentration by Control of the amount of silicon to be added is adjustable.

In another aspect of the invention is the semiconductor nitride layer etching system characterized by a device addition of fluorine to the treatment solution to achieve the  Silicon concentration in the treatment solution Control of the amount of fluorine to be added.

According to a further aspect of the invention is the semiconductor nitride layer etching system characterized by a device tion to add fluorine to the treatment solution so that the silicon concentration in the treatment solution to a certain rate of silicon saturation concentration at the The temperature of the treatment solution is adjustable.

According to another aspect of the invention, a semi-lead ternitride layer etching system provided, the characterized is characterized by a device for cooling and draining a treatment solution that is mainly phosphoric acid contains, from a treatment tank and a facility to inject fresh phosphoric acid solution into it Container so as to contain the components of the treatment solution the container.

In another aspect of the invention is the semiconductor Nitride layer etching system characterized in that the Silicon concentration in the treatment solution in one Treatment container by injecting fresh phosphorus acid solution containing silicon is adjustable.

According to another aspect of the invention is the semiconductor nitride layer etching system characterized by a heat Exchanger for heat transfer between the to be removed Phosphoric acid treatment solution and Phos to be injected phosphoric acid solution.

According to another aspect of the invention, a semi-lead ternitride layer etching system provided, the characterized is characterized by a large number of treatment containers, in which a treatment solution is included, the contains mainly phosphoric acid and also silicon, so that the silicon concentration in the in the treatment  container received treatment solution by transfer of treatment solution between the treatment containers is adjustable.

According to a further aspect of the invention, the semi-lead is ternitride layer etching system characterized by a Control device for the silicon concentration of the treatment solution in the treatment containers and calculate the Transfer of treatment solution between treatments to control containers.

In another aspect of the invention is the semiconductor nitride layer etching system characterized by a device device for measuring the relative density of the treatment solution, the relative density of the treatment solution by adding of water.

According to another aspect of the invention, the semiconductor Nitride layer etching system, characterized in that a Treatment container and a chemical solution in touch area of a circulation channel for chemicals solution made of a material from which no silicon is extracted.

According to yet another aspect of the invention, those are above Combine listed features of the invention bar.

The invention is also described below with respect to others Features and advantages based on the description of exec example and with reference to the enclosed Drawings explained in more detail. The drawings show in:

. Figure 1 shows the configuration of the first embodiment of the nitride layer etching system (Naßbehandlungssystems) according to the invention;

Fig. 2, in which a nitride layer is etched with the first embodiment of the invention, the cross sectional shape of a device wherein a case is shown;

FIG. 3 shows the relationship between etching rates of a plasma silicon nitride film (Plasma-SiN), and a layer of oxide (TEOS) gas on the one hand and the F concentration in a phosphoric acid system on the other hand;

FIG. 4 shows the configuration of the second embodiment of the nitride layer etching system (Naßbehandlungssystems) according to the invention;

FIG. 5 shows etching rates of SiON layers having different refractive indices with respect to hot phosphoric acid;

Figure 6 shows the relationship between the total thickness of the treated layer of a nitride layer and the Si concentration in a phosphoric acid system.

Figure 7 shows the relationship between the Si concentration in a phosphoric acid system and etching rates of Si₃N₄ and SiO₂.

Figure 8 shows the relationship between the useful life of phosphoric acid and etching rates of Si₃N₄ and SiO₂.

Fig. 9 shows the relationship between the phosphoric acid temperature and the Si saturation concentration;

Fig. 10 (= 1.590 refractive index), acid temperature, the etch rate of an SiON layer at any temperature when the Si concentration in phosphoric acid to 0% and 25% of the Si-saturation concentration is set at each phosphorus;

Figure 11 shows a comparison between increasing amounts of Si in phosphoric acid, if a managed forming with liquid in the contact region of Ti or is made of quartz.

Fig. 12 shows the configuration of the third embodiment of the nitride layer etching system (Naßbehandlungssystems) according to the invention;

Fig. 13 in detail the structure of a heat exchanger;

Fig. 14 shows the relationship between the etching rate of SiO₂ and the life of the treatment solution when the concentration of Si injected in phosphoric acid is adjusted and when Si is injected quantitatively in phosphoric acid;

Fig. 15 shows the configuration of the fourth embodiment of the nitride layer etching system (Naßbehandlungssystems) according to the invention;

16 shows the relationship between the concentration and electric conductivity of phosphoric acid.

Fig. 17 shows the relationship between the concentration and the boiling point of phosphoric acid;

Fig. 18 shows the relationship between the temperature and the etching rate of phosphoric acid;

Fig. 19 shows the results of experiments on the relationship between the presence or absence of control of the relative density and the etching rate of phosphoric acid;

. 20 shows the configuration of the fifth embodiment of the nitride layer etching system (Naßbehandlungssystems) according to the invention; and

Fig. 21 shows the configuration of a conventional nitride-film etching system (Naßbehandlungssystems).

First embodiment

The first embodiment will be described below, in which the emphasis is on the choice of the treatment solution and the adjustment of the fluorine concentration in the treatment solution. Fig. 1 shows a configuration of the first exporting approximate shape of the etching system (Naßbehandlungssystems) for etching a semiconductor nitride layer. As shown in FIG. 1, the wet treatment system comprises a treatment tank 1 and a pump 2 to circulate the treatment solution through the treatment tank 1 . A circulation channel for the treatment solution comprises a filter 3 to remove impurities from the treatment solution, a heating device 4 to bring the temperature of the treatment solution back to a treatment temperature, and a drip device 5 for demineralized water to fill up water to be evaporated.

Furthermore, the wet treatment system has a fluorine or F concentration monitor 7 , which monitors the fluorine or F concentration in the treatment solution and controls a fluorine or F injector 10 in order to increase the F concentration in the treatment solution . The information from the F concentration monitor 7 is transmitted to an injection control system 8 on a signal line 12 . The injection control system 8 controls the F-injector 10 via a signal line 14 .

The wet treatment system works with phosphoric acid as the main component of the treatment solution, heats the treatment solution by means of the heating device 4 to keep it at a constant temperature, and keeps the concentration of the phosphoric acid constant while at the same time water to be evaporated from the drip device 5 for demineralized water is refilled. In addition, the wet treatment system causes the constant circulation of the treatment solution by the pump 2 to accelerate movement effects.

The treatment solution to be added to the phosphoric acid becomes described below. After experiments it is difficult to maintain the state in which Si compounds completely from a phosphoric acid solution are removed. It is more important the F concentration keep more stable than the Si compounds completely remove.

By adding ammonium fluoride (NH₄F) or buffered Hydrofluoric acid (BHF), the hydrofluoric acid (HF) and Contains ammonium fluoride (NH₄F) to a phosphoric acid solution is the following reaction equation as one Get equilibrium reaction:

NH₄F + HF ↔ NH₄ + HF₂⁻

It is thus possible to adjust the concentration of HF₂, which as Etchant for SiO₂ serves to keep stable in phosphoric acid, by using instead of hydrofluoric acid BHF, the NH₄F and HF contains, is added. Furthermore, since the concentration of HF₂, which serves as an etchant, can be controlled more precisely, is the addition of ammonium fluoride (NH₄F) or buffered Hydrofluoric acid (BHF), which contains HF and NH₄F, for the setting of the F concentration is essential.

Silicon serves as a substrate to form an integrated circuit. The etching of silicon is progressing the boundary between silicon grains continues, and the roughness increases because grains are activated. An increase in Roughness leads to the problem of worsening Characteristics of a device because of the leakage current very increases slightly and the breakdown voltage is reduced.  

A case is known in which to etch silicon or a silicon nitride layer a mixture of phosphoric acid, Hydrofluoric acid and nitric acid is used. The However, inventors have found that the silicon etch rate can be controlled to 1 Å / min or less if the Nitric acid components are removed, so that the Etching rate is reduced. As a result, there will be no increase the roughness is observed or there is no deterioration characteristics.

In the present case, therefore, the F concentration in the treatment solution is recorded by the F concentration monitor 7 , the injection control system 8 is actuated in response to a signal from the monitor, and ammonium fluoride (NH₄F) or buffered hydrofluoric acid (BHF), the hydrogen fluoride (HF ) and contains ammonium fluoride (NH₄F) is added from the F injection device 10 to control the F concentration. It is thereby possible to stabilize the nitride layer etching rate.

The importance of controlling the concentration of fluorine or ammonium fluoride in a phosphoric acid mixture, ie in the present case of F concentration, is shown below described. As a specific application example the importance of controlling the F concentration to 200 ppm or less for etching a plasma silicon nitride layer (Plasma SiN).

Fig. 2 shows a structure in which a nitride layer is formed by plasma (plasma SiN film) is etched. This is a case in which a nitride layer formed by plasma as a reflection-reducing layer of a semiconductor component with a 0.25 μm standard, which is a further developed component such as a 256 MDRAM, is etched and removed.

In the manufacturing process of the 256 MDRAM, as shown in FIG. 2, a TEOS oxide film is formed on a silicon substrate, and then plasma SiN serving as an anti-reflection film is formed on the TEOS oxide film. Then resist is applied to the wafer and exposed to form a hole with a diameter of 0.25 µm (2500 Å) on the TEOS oxide layer. After removing the resist lacquer, the component has the structure shown in FIG. 2.

In the above process, the plasma SiN is generally etched and removed by fluorine-containing phosphoric acid. The etching time is 30 s or more in terms of etching uniformity and controllability. Fig. 3 shows the relationship between the etching rates of plasma SiN and an oxide layer (formed by TEOS gas) and the concentration of F contained in a phosphoric acid system in the etching treatment using a fluorine-containing phosphoric acid.

The structure shown in FIG. 2 applies generally to a component with a 0.25 μm standard, and a layer thickness of the plasma SiN of approximately 700 Å is selected with a view to an absorption coefficient dependent on an exposure wavelength. To remove the layer of 700 Å in thickness for 30 seconds or more, it is found from the results of experiments shown in FIG. 3 that the etching rate is 1400 Å or less for 1 minute and the F - concentration must be 220 ppm or lower. During the etching process of the plasma SiN layer, the TEOS oxide layer is laterally etched away from the transverse direction. From the experimental results of Fig. 3 it follows that the etching depth is 125 Å / min from both sides, and that the diameter increases by 250 Å / min. The tolerance to form a hole with a diameter of 2500 Å is 10% of the diameter, ie 2500 ± 250 Å. If the F concentration is higher than 200 ppm, the oxide layer is etched to more than 250 Å or more to exceed 250 Å.

It is therefore not possible to use a hole a diameter for a component according to the 0.25 µm Standard is required to meet. If the F concentration Is 200 ppm or lower, the above problem becomes solved because the etching conditions for the plasma SiN layer (700 Å for 30 s or longer) and for the TEOS layer (250 Å or less) are satisfied by etching between 30 s and 1 min is carried out.

Second embodiment

The following describes the second embodiment in which the adjustment of the silicon concentration in the treatment solution is important. Fig. 4 shows a configuration of the etching system (wet treatment system) according to this second embodiment. As FIG. 4 shows, the wet treatment system includes a treatment tank 1 and a pump 2 for circulating the treatment solution through treatment tank 1. The circulation channel for the treatment solution has a filter 3 to remove impurities from the treatment solution, a heating device 4 to bring the temperature of the treatment solution back to the treatment temperature, and a drip device 5 for demineralized water to renew the water to be evaporated.

Furthermore, the wet treatment system has a Si concentration monitor 6 for detecting the Si concentration in the treatment solution and an F concentration monitor 7 for detecting the F concentration in the treatment solution. An injection control system 8 is actuated in response to signals from these monitors to control an Si injector 9 to increase the Si concentration in the treatment solution and an F injector 10 to increase the F concentration in the treatment solution. The information from the Si concentration monitor 6 is transmitted to the injection control system 8 on a signal line 11 , and the information from the F concentration monitor 7 is transmitted to the injection control system 8 on a signal line 12 . The injection control system 8 controls the Si injector 9 via a signal line 13 and the F injector 10 via a signal line 14 .

The wet treatment system uses phosphoric acid as the main component of the treatment solution, heats the treatment solution by means of the heating device 4 to keep it at a constant temperature, and keeps the phosphoric acid concentration constant while at the same time water to be evaporated from the dropping device 5 for demineralized water is refilled. Furthermore, the treatment solution in the wet treatment system is constantly circulated by the pump 2 in order to accelerate movement effects.

In the present case, the meaning of the addition of Si will first be explained. When element separation is performed by an oxide layer of a silicon device, a method of forming a very thin oxide nitride layer about 10 nm thick under a nitride layer can be used. In this case, since the nitride layer is frequently etched with a hot treatment solution based on phosphoric acid, it is necessary to rule out that the hot treatment solution based on phosphoric acid comes into contact with a silicon substrate and attacks the substrate. If the etching rate of the oxide nitride layer is greater than that of the nitride layer, the oxide nitride layer is removed immediately after the nitride layer is removed. Therefore, a larger selectivity ratio between these two layers is better. Fig. 5 shows etching rates of SiON layers having different refractive indices with respect to hot phosphoric acid. As shown in Fig. 5, the etching rate of an oxide nitride layer tends to decrease with increasing silicon concentration, but the etching rate of a nitride layer does not change. That is, high selectivity can be obtained by keeping the silicon concentration high.

The importance of injecting Si into the phosphoric acid solution and adjusting the Si concentration, and the importance of injecting F into the phosphoric acid solution and adjusting the F and Si concentrations in the present case are described below. In the case of the system shown in FIG. 4, when the etching is carried out in the treatment tank 1, the Si component dissolves and the Si concentration in the treatment solution increases. This state is shown in Fig. 6. As can be seen there, the silicon saturation concentration increases with the increase in the total dissolved layer thickness. The Si influences the etching rate of SiOxNy-based layers such as an SiO₂ layer, an LP-SiON layer, a plasma SiON layer, a plasma SiN layer or an N-doped polysilicon layer and causes depending on the circumstances, a 100-fold or higher fluctuation in the rate. This is shown in Fig. 7. From Fig. 7 it can be seen that the etching rate of Si₃N₄ hardly changes with a change in the silicon concentration, whereas the etching rate of SiO₂ decreases extremely.

The conventional methods have no way of conveying generated Si-based impurities out of the system. Thus, as shown in Fig. 7, when the etching rate fluctuates during the treatment, the etching of a desired layer thickness is not completed within a predetermined time according to the circumstances, and therefore a residual layer is formed.

An evaluation made by the inventor has shown that Reactions that take place in phosphoric acid solution, like after can be arranged standing:

Si₃N₄ + 12H₂O ↔ 3Si (OH) ₄ + 4NH₄ ↑ (a)

SiO _2Ä + 2H₂O ↔ Si (OH) ₄ (b)

As the above equations (a) and (b) show, an Si containing layer using H₂O as an etchant etched, and Si is treated in the form of a hydrate solution accumulated. If the amount of Si accumulated in the reaction system increases, reactions continue left in equations (a) and (b), specifically in equation (b), and SiO₂ remains as a residue layer.

The wet treatment system of the second embodiment is so built that a fluorine-containing treatment solution in a circulating treatment solution can be injected. Reaction equations when F is injected are below specified. If F ions are added, they run on pending reactions:

SiO₂ + 4F⁻ + 2H₂O → SiF₄ ↑ + 2OH⁻ (c)

SiF₄ + 2F⁻ + 2H₂O → H₂SiF₆ ↑ + 2OH⁻ (d)

As a result, Si, which inhibits the etching process, becomes Verunreini conditions in the Si system in the form of H₂SiF₆ removed. At the same time, F ions inhibit the generation of a residual layer, because they etch a SiO₂-based layer and remove it accelerate. It is believed that the discharge from the System in the form of SiF₄ gas, as in equation (c) ge shows, and in the form of an azeotrope of H₂O with H₂SiF₆, as shown in equation (d).

As shown here, impurities in the SiO₂ system are removed from the system by adding F. However, this embodiment also makes it possible to detect the Si concentration in the phosphoric acid solution using the Si concentration monitor 6 and the F concentration in the solution using the F concentration monitor 7 , and to calculate a required amount of Si and / or F by to inject the Si injector 9 and / or the F injector 10 using the injection control system 8 .

Since the conventional method is no way to stop wearing Si from the system, it is not possible Remove impurities in a positive way, so that the Performance of the treatment solution with time ver gets worse. The present second embodiment However, it enables the operating behavior of the treatment stabilizing solution and using it for a long time add a mechanism for discharging Si from the System is provided.

The result of applying this embodiment to a built etching system is described below. As will be explained in connection with Fig. 7, the SiO₂ etch rate decreases as the silicon concentration increases. However, the present system stabilizes the etching rates of Si₃N₄ and SiO₂ by adding F and keeping the Si concentration constant. LP-Si₃N₄ and SiO₂ as representative of layers based on SiOxNy are selected, and this embodiment is applied for LP-Si₃N₄ and SiO₂. The result is shown in Fig. 8. So since it is possible to keep the etching rates of LP-Si₃N₄ and SiO₂ constant, the shape of a component is also kept constant.

The importance of setting an Si concentration based on the saturated Si concentration corresponding to the temperature of the phosphoric acid solution will be described below by further developing the setting of the Si concentration. Currently, the phosphoric acid treatment temperature changes depending on the variety of layer qualities, and different treatment temperatures between 100 and 200 ° C are used. The Si saturation concentration changes depending on the temperature of the phosphoric acid serving as a solvent. Experimental results in this regard are shown in FIG. 9. As the test results from FIG. 9 show, only 40 ppm silicon dissolves in phosphoric acid at 120.degree. If an Si₃N₄ layer is treated under these conditions, a high selectivity ratio for SiO₂ can be obtained. However, it has been found that the Si₃N₄ layer cannot be used in practice because a state of oversaturation occurs and the system is subject to interference if a filter becomes clogged, or interference to the method occurs because residues remain on a wafer .

To solve the above problem, it has been found that it is important to adjust the Si concentration to a specific to control the rate of Si saturation concentration clearly based on the phosphoric acid temperature the Si saturation concentration is determined. By application this method it is possible to change the selectivity ratio to keep in an optimal, constant range.

In the case of the nitride film etching system containing only phosphoric acid at an F concentration of 0 ppb as shown in Fig. 10, the temperature of the phosphoric acid must be set to 150 ° C or lower in order to reduce the etching rate of plasma SiN at 200 Å / min, which is considered a finely controllable value in a process, or lower. The Si saturation concentration at 150 ° C is 75 ppm. In order to achieve a selectivity ratio of 100 or greater in this process, the etching rate of a SiON layer to be etched simultaneously must be 2 Å / min or less. This condition is met at 19 ppm or more, which is 25% or more of the Si saturation concentration.

There is a positive correlation between temperature phosphoric acid and Si saturation concentration.  

In addition, the etch rate of each layer is a function of the Si concentration and can be standardized as a function of the percentage of the saturation concentration of the Si concentration. This is shown in Fig. 10. Therefore, it is concluded that the selectivity ratio can be controlled by controlling how much Si has already been dissolved or how much Si can be dissolved by preparing it with the saturation concentration at the treatment temperature. In the above description, a case is described in which the F concentration is 0 ppb. However, it is certain that the same trend exists even if fluorine is contained in the phosphoric acid.

The treatment solution below is for use with the embodiment described. It is important that F concentration in phosphoric acid and the Si concentration to a predetermined rate of Si saturation concentration at the then prevailing temperature of the phosphoric acid to deliver. After trying it is difficult to maintain the state in which Si compounds are complete dig are removed from the phosphoric acid, and it is from Weight point of setting the F concentration and the Adjustment of the Si concentration is necessary so that the F- Concentration and the Si concentration to the desired one Percentage of the Si saturation concentration at a ge given temperature of phosphoric acid are more stable.

In the case of ammonium fluoride (NH₄F) and buffered fluorine hydrochloric acid (BHF), which contains HF and NH₄F, applies reaction equation below as an equilibrium reaction:

NH₄F + HF ↔ HN₄ + HF₂⁻

So if instead of hydrofluoric acid NH₄F or BHF, which contains HF and NH₄F, it is possible to HF₂ concentration, which as the etchant for SiO₂ in Phos  phosphoric acid serves to keep more stable. Furthermore, since the HF₂-Kon concentration can be controlled more precisely is the addition of NH₄F or BHF to adjust the F concentration effective.

In the present embodiment for setting the Concentration of silicon in the treatment solution is contained, the ent mainly hot phosphoric acid holds, the treatment solution is not on such solutions limited to only ammonium fluoride or buffered fluorine contain hydrochloric acid in phosphoric acid solution. The Treatment solution cannot just be hot phosphoric acid alone use, but also a solution by adding obtained from hydrofluoric acid to hot phosphoric acid becomes. It becomes a wet treatment system from the above hot phosphoric acid system applied with the addition of Silicon or a silicon compound to the concentration to control the silicon or silicon compound. It is possible, silicon in the form of SiO₂ granules, SiO₂- Powder or SiO₂, which is dissolved in demineralized water is to be added, but silicon is preferred in the form of added colloidal silicon because of the colloidal silicon easily reacts to other substances.

It is explained below that simple control of the Si concentration by injecting F can also be done by the system shown in FIG. 1. The wet treatment system shown in Fig. 4 adds F ions depending on the concentration of Si-based impurities. The wet treatment system of the first embodiment shown in Fig. 1 is functionally limited to the detection and addition of F ions. Even if the system is simplified as mentioned above, it may be possible to determine the etching selectivity ratio between a nitride layer, which serves as a layer to be etched, and a further layer which is present at the same time (e.g. a layer based on SiOxNy: Ox, y2) to keep in a certain range. For example, there is a case where the Si released from a lot to be treated is constant over every lot so that the amount of Si in a system can be estimated. In this case, the selectivity ratio can only be kept constant by adding F ions and the system can also be simplified.

It is described below that in the system of Fig. 4, a large or small selectivity ratio can be selected by setting the Si concentration to a high or low value depending on the kind of the material to be treated. For example, the silicon concentration is adjusted to a certain range of a low concentration of 50% or less, and a lot is treated with a small selectivity ratio. When the silicon concentration of the processing solution becomes higher, it is adjusted to a certain range of 50% or more, and other batches are treated with a high selectivity ratio. A treatment container can thus be used for various purposes. By using a large number of treatment containers or etching systems and by setting different silicon concentrations, it is also possible to carry out parallel treatments. This will be described in more detail.

The following describes the meaning of a material that comes into contact with the treatment solution in a treatment tank or a circulation system in the embodiment of FIG. 4. In the above embodiment, it is described that it is important to control the Si concentration to a desired percentage of the Si saturation concentration at the specific temperature. Since the surfaces of a heating device and a container used are currently made of quartz, the amount of Si released from the surface cannot be neglected. While there have been instances where SiC has been used and quartz has been avoided, there is still Si in each case. Fig. 11 shows the rates of increase of Si in phosphoric acid when the heater and the container are made with Ti or when they are made with conventional quartz parts. By manufacturing the system with Ti or its alloys or with a material other than quartz, such as SUS316 or its electrolytically polished material, it is possible to reduce the adverse influence of Si on the etching rates. It is important in the present case, which is a process using high temperature phosphoric acid with the addition of fluorine, that a treatment tank and a circulation system are made of a material from which no Si is dissolved.

Third embodiment

The third embodiment in which the discharge and injection of the treatment solution and the adjustment of the silicon concentration are important will be described below. Fig. 12 shows a configuration of the etching system (the Naßbehand development system) according to this third embodiment. The wet treatment system has a treatment tank 1 , a pump 2 for circulating the treatment solution through the loading container 1 , a filter 3 to remove impurities from the treatment solution, a heater 4 to return the temperature of the treatment solution to the treatment temperature, and a Drip device 5 for de-mineralized water to refill water to be evaporated.

The Naßbehandlungssystem further comprises a Si-Konzentra tion monitor 6, which detects the Si concentration in the treatment solution, and a F concentration monitor 7, detects the F concentration in the treatment solution. An injection control system 8 is actuated in response to signals from these monitors and controls an Si injector 9 to increase the Si concentration in the treatment solution and an F injector 10 to increase the F concentration in the treatment solution. The information from the Si concentration monitor 6 is fed to the injection system thereby control 8 on a signal line 11, and the information from the F-concentration monitor 7 is supplied to the injection control system 8 leads to a signal line 12 supplied. The injection control system 8 controls the Si injector 9 via a signal line 13 and the F injector 10 via a signal line 14 . The above units and operations correspond to those of the system of the first embodiment shown in FIG. 1 and are therefore not described in detail.

The wet treatment system of the third embodiment is further constructed so that the treatment solution can be discharged from a part of a treatment solution circulation channel through a heat exchanger 16 to an outlet 15 , and phosphoric acid can be added through a heat acid addition line 17 through the heat exchanger 16 .

On the other hand, in the second embodiment shown in FIG. 4, Si-related impurities are removed by adding F ions. In the case of the wet treatment system of the third embodiment shown in FIG. 12, the heat exchanger 16 is also arranged on the upstream side of the outlet 15 . Thus, a mechanism for discharging a part of the Si-containing phosphoric acid from the system is provided in addition to the construction corresponding to that of the second embodiment shown in FIG. 4, and phosphoric acid free of impurities is supplied to the system so as to Control Si concentration in the system to a desired value or below. In addition, heat from the phosphoric acid containing Si-related impurities is given off by the heat exchanger 16 to the phosphoric acid free of impurities.

Thus, the function of removing Si is additional related impurities and it is possible that etch selectivity ratio between a nitride layer, which serves as a layer to be etched, and another, ko existing layer (e.g. a layer based on SiOxNy: Ox, y2) to keep constant over a long time. Furthermore, that Phosphoric acid exchange system according to this embodiment arranged at every point of the phosphoric acid circulation system and the amount of Si to be removed by F can be ver be wrested.

Thus, since the wet treatment system according to the third embodiment is provided with a phosphoric acid exchange system in addition to the functions of the wet treatment system of Fig. 1, the Si concentration in the treatment solution can be precisely controlled so that the functions of the first and third Embodiment are combined. In addition, depending on the circumstances, the phosphoric acid exchange system can be used independently.

In the case of the system of Fig. 12, the phosphoric acid solution to be discharged is cooled by the phosphoric acid solution to be injected. If the circumstances so require, it is also possible to cool the phosphoric acid solution to be discharged with water which is added to a treatment tank or the circulation system. In addition, a case is conceivable in which the phosphoric acid solution is only cooled with cooling water and the cooling water is drained off without introducing it into the circulation system. Furthermore, it is also possible to additionally provide a cooling function by cooling water on the system of FIG. 12 in order to carry out complete cooling.

The heat exchanger used in the system of Fig. 12 is described below. Fig. 13 shows the details of the heat exchanger of Fig. 12. The treatment solution, which has the treatment temperature, is derived for heat exchange in the drain line 15 a. The solution flows under heat transfer through the drain line 15 b, which passes through the heat exchanger 16 so that its specific surface is increased. The heat exchanger 16 is filled with normal temperature treatment solution which is injected through a normal temperature phosphoric acid addition tube 17 a. Therefore, the treatment solution in the drain line 15 b is continuously cooled and discharged from the drain line 15 c.

The treatment solution thus heated is fed to a treatment tank through a supply line 17 c for heated phosphoric acid. These areas in contact with liquid must consist of a highly acid-resistant and highly heat-resistant metal such as PVDF, PFA or a metal that is free of metallic impurities.

The importance of setting the Si concentration in Phos phosphoric acid to be added at the treatment temperature will be described below. The Si concentration in the Phosphoric acid takes off during the etching treatment of lots to. The Si concentration is effective to the Selek to improve the activity ratio between Si₃N₄ and SiO₂, but it has the disadvantage that it has the life of the Treatment solution shortened. The main reason here is that the system filter becomes clogged.

Therefore, as described in the second embodiment, in order to control the Si concentration to a setting range of a rate of the Si saturation concentration such as 25 to 90% at the treatment temperature, it is possible to extend the service life of the treatment solution by changing the Si concentration into of the phosphoric acid to be added is adjusted or slowly reduced as the number of batches treated increases. Fig. 14 shows the above case. As a result of the adjustment, the usage time of the treatment solution is extended up to three times. It is concluded from this test result that it is important not only to add Si to the phosphoric acid but also to adjust the amount of Si. In this case, as described in the second embodiment, the service life of the treatment solution is further extended by adjusting the F concentration, and it is possible to maintain a selectivity ratio in the desired range over a longer period of time.

Fourth embodiment

The fourth embodiment will be described below, in which special emphasis is placed on controlling the relative density of the treatment solution and adjusting the concentration of the treatment solution. Fig. 15 shows a con figuration of the etching system (the Naßbehandlungssystems) according to this fourth embodiment. The nitride film etching system has a selectivity ratio control function and is able to control the specific gravity of phosphoric acid to which F ions are added. The relative density of the treatment solution depends on its concentration and the density of the substances it contains, such as silicon. Therefore, controlling the relative density of the phosphoric acid solution represents controlling the phosphoric acid concentration.

The system shown in Fig. 15 according to the fourth embodiment is basically the same as the system of the first embodiment of Fig. 1. Here, the same or equivalent parts are given the same reference numerals, and a detailed description of these parts is omitted. The system in FIG. 15 has a control function for the relative density in addition to the functions of detecting the F ion concentration and the F ion addition described in FIG. 1. SiF₄ or H₂SiF₆ containing vapor evaporates, and F ions are present in the phosphoric acid. Therefore, a float 26 , the surface with high resistance to hydrofluoric acid, for example made of PVDF or coated with PVDF, is arranged on an overflow tank. A lid 27 that is resistant to hydrofluoric acid is placed on the container to separate it from a relative density detector 28 positioned on the lid 27 . Since the optical system of the relative density detector is arranged near a level measuring rod 29 which is directly connected to the float 26 , it is possible to visually check the relative density. Here, if the substance to be injected is hydrofluoric acid, a function for correcting the specific gravity of hydrofluoric acid must be used because the specific gravity is 1.13 compared to that of water which is 1.

The relative density can also be controlled by a conductivity control as well as with the density meter according to FIG. 15. In addition, it is possible to control the relative density by using a conductivity meter, which is resistant to hydrofluoric acid, in the treatment tank 1 . Fig. 16 shows the relationship between the phosphoric acid concentration and the conductivity. The relationship of Fig. 16 can be applied directly in the case of a solution containing only phosphoric acid. However, when an additive is added to the phosphoric acid, the relationship must be used by shifting it up to a value equal to the influence of the phosphoric acid mixed with the additive.

As described above, the hot phosphoric acid is used Ending wet treatment system with a control system the relative density of the treatment solution, where at the relative density at an overflow area of the treatment solution or a downward area and the dilute phosphoric acid or water or the fluorine-containing solution becomes the treatment solution added. It also has a system for measuring the relative A density meter placed on an overflow area of the Treatment solution or a downward area  swims and has a unit capable of an electrical value indicated by the density meter, to read physically or optically.

As a means for controlling the concentration of phosphoric acid, it is further preferred that the relative density to be controlled is kept within ± 3% of water-saturated phosphoric acid at the temperature of the treatment solution. The reason here will be described below. First, it is described in the first embodiment with reference to FIG. 12 that the precision of the component manufacturing dimensions must be set to at least ± 10%. The relative density of phosphoric acid then corresponds to the concentration of phosphoric acid in a ratio of 1: 1. The concentration also clearly determines the boiling point of phosphoric acid. Fig. 17 shows the correlation between the concentration and the boiling point of phosphoric acid. From Fig. 17 it can be seen that the boiling point is between ± 15 ° C or more when the phosphoric acid concentration is between ± 3% at a treatment temperature of 160 ° C, as is often used for the phosphoric acid treatment. Fig. 18 shows the correlation between the phosphoric acid temperature and the etching rate. From Fig. 18 it can be seen that the etching rate of a Si₃N₄ layer between ± 5 ° C at a treatment temperature of 160 ° C changes from 40 A / min to 50 Å / min and with an average value of about 45 Å / min lies. In order to comply with the ± 10% limitation for the manufacture of components, the relative density must be controlled within at least ± 3%. Fig. 19 is a graph showing results of an experiment as to whether an etching accuracy of ± 10% can be maintained when the relative density of the phosphoric acid is controlled to ± 3% or the control of the relative density is not applied. In the case of the experiment in which the phosphoric acid concentration is controlled within ± 3%, the etching rate is 56 ± 3 Å / min and is kept within ± 10%. On the other hand, if no control is performed within ± 3%, the etching rate is found to be between ± 10% or more.

As described above, the wet treatment system is using hot phosphoric acid with a device provided to measure the relative density by measuring the relative density of the treatment solution at an overflow area of the treatment solution or a downstream thereof area and measure around water, diluted Phosphoric acid or the water containing F or diluted Add phosphoric acid to the treatment solution. It also has the device for measuring the relative density yourself temesser on an overflow area of treatment solution or a downstream area swims, and has a unit capable of one of electrical, physical, or to read optically. Furthermore, the relative density of the Controlled phosphoric acid so that it within + 3% of relative density of phosphoric acid saturated with water is kept at the temperature of the treatment solution.

Fifth embodiment

The fifth embodiment in which a plurality of treatment containers are provided will be explained below. Fig. 20 shows a configuration of this etching system (wet treatment system). As shown in FIG. 20, the wet treatment system is constructed by providing the same system as the wet treatment system shown in FIG. 4 in two interconnected stages, one system being a treatment unit A and the other system being a treatment unit B. In Fig. 20, the same reference numerals as in Fig. 4 are used for the same or equivalent parts or areas (each with the subscript "a" or "b"). The exact description can therefore be found in the description of FIG. 4.

The fifth embodiment of the wet treatment system, however, has a treatment solution channel which leads from a treatment tank 1 a to a treatment tank 1 b via a valve 18 a, a pump 19 a and a silicon adjustment unit 20 . Furthermore, a channel runs from the circulation channel of the treatment container 1 b to an outlet 15 b through a valve 18 b and a pump 19 b. A control unit 21 is designed so that it receives the information for a batch 22 via an interface 23 , and controls the valve 18 a, the pump 19 a, the valve 18 b and the pump 19 b via control lines 24 and 25 .

The wet treatment systems shown in FIGS . 1, 4 and 12 according to the first, second and third embodiments keep the etching selectivity ratio in each individual container constant. The wet treatment system of the fifth embodiment shown in Fig. 20 has a plurality of containers. However, to simplify the description, this system is explained as a two-container system.

The wet treatment system of the fifth embodiment carries out the treatment with a low-Si treatment solution and by etching with a small selectivity ratio in the treatment container 1 a of the treatment unit A and carries out the treatment with a high-Si treatment solution and by etching with a large selectivity ratio in the treatment container 1 b of treatment unit B. For example, it should be assumed that the Si concentration for the treatment tank 1 a with 0 to 70 ppm and for the treatment tank 1 b with 50 to 120 ppm is set.

The system starts using the treatment solution in the treatment tank 1 a. The Si concentration in the treatment container 1 a increases with progressing wafer treatment. The increasing Si concentration is calculated and estimated depending on the lot treatment data of lot 22 (e.g. history, treatment layer thickness, number of wafers and process). For example, the data of the lot 22 are read into the control unit 21 through the interface 23 in order to calculate the increase in Si. When it has been calculated that the Si concentration reaches the default value of 70 ppm, the valve 18 a is opened by the control line 24 to drive the pump 19 a. Si-rich treatment solution is injected into the treatment tank 1 b. The treatment tank 1 b enables a treatment to be carried out using a treatment solution having an Si concentration of 70 ppm or more. SiOxNy etching with small and large selectivity ratios can thus be carried out by a wet treatment system.

The following procedure can also be performed. If the control unit 21 determines that the treatment solution in the treatment tank 1 b with progressive batch treatment is outside the default state, the supply of a new batch to the treatment tank 1 b is stopped. The treatment solution is prepared by opening the valve 18 b for driving the pump 19 b is derived, and then b 18 water is supplied by closing the valve. The control unit 21 decides whether the treatment solution in the treatment container 1 a speaks the desired condition. If the treatment solution meets the condition of a Si concentration of 50 ppm or more, it is injected directly into the treatment tank 1 b. This decision can also be made by the Si concentration monitor 6 a. Even if the Si concentration of 50 ppm, the condition is not reached, it is possible to adjust the concentration to the condition by 9 b Si is added by the Si-setting unit 20 or the Si-injector.

The phosphoric acid exchange device of this embodiment can form at any position of a phosphoric acid circulation systems, or it can be used independently  or with the F injection system, the Si injection system or the flow of the first to third embodiments be combined.

Using a variety of containers at the same time So it is possible to keep the Si concentration in a container to 50% or less of the saturation concentration at the limit the desired temperature and the Si concentration in another container to 50 to 90% of the Si concentrations limit tration at the desired temperature and selective etching with small or large selectivity ratio apply.

In the case of FIG. 20, two treatment units (ie two treatment containers) are connected to one another, but it is also possible to connect two or more required containers to one another. In this case, treatment solution is transferred to a container of the next in-line stage or is transferred normally between individual treatment containers. In the case of the example of Fig. 15, the treatment unit has the same configuration in each stage. However, it is also possible to use treatment units with different configurations. Furthermore, containers can be connected to one another by a treatment solution channel (for example a pipeline), or treatment solution can be transferred in batches between independent treatment units in each case.

The invention is described above with reference to five Embodiments described. However, these are each related. The features of each embodiment can therefore also be combined, and in addition to each separately shown embodiment can be a variety of Etching systems can be realized.

As described above, the invention specified a silicon nitride layer etching system with which it  it is possible to include the etching rate of a silicon nitride layer position and control and perform a stable etching, by the treatment solution used in the system, the main one contains, adjusted and controlled becomes. Furthermore, an etching system is provided by the invention give, where it is possible, the selectivity ratio to control so that the etch selectivity ratio of treating layers is set and controlled.

The present application is based on the JP patent application 8-81176, filed April 3, 1996 in Japanese Patent Office, and their overall content is summarized here introduced.

Claims (16)

1. Semiconductor nitride layer etching system, characterized by a device ( 1 ) for adding ammonium fluoride or buffered hydrofluoric acid to a chemical solution which mainly contains hot phosphoric acid solution. 2. Semiconductor nitride layer etching system according to claim 1, characterized in that a device ( 7 ) is provided to detect the fluorine concentration in the chemical solution, so that the fluorine concentration is adjustable by controlling the amount of fluorine to be added. 3. The semiconductor nitride layer etching system according to claim 2, characterized, that the fluorine concentration in the chemical solution 200 ppm or less is controllable.   4. semiconductor nitride layer etching system, characterized by a device ( 9 ) for the addition of silicon or a silicon compound to a chemical solution which mainly contains phosphoric acid solution. 5. Semiconductor nitride layer etching system according to one of claims 1 to 3, characterized in that a device ( 9 ) is provided for adding silicon or a silicon compound to the chemical solution. 6. Semiconductor nitride layer etching system according to one of claims 4 or 5, characterized in that a device ( 6 ) for detecting the Siliciumkon concentration is provided in the chemical solution, so that the silicon concentration is adjustable by controlling the amount of silicon to be added. 7. A semiconductor nitride layer etching system according to one of claims 4 or 5, characterized in that a device ( 7 ) for adding fluorine to the chemical solution is provided so that the silicon concentration in the chemical solution can be adjusted by controlling the amount of fluorine to be added. 8. Semiconductor nitride layer etching system according to one of claims 4 or 5, characterized in that a device ( 7 ) for adding fluorine to the chemical solution is provided so that the silicon concentration in the chemical solution to a certain rate of the silicon saturation concentration the temperature of the chemical solution is adjustable. 9. semiconductor nitride layer etching system, characterized by a device ( 15 ) for cooling and discharging a chemi kalienlösung, which mainly contains phosphoric acid solution, from a treatment container and a device ( 17 ) for injecting fresh phosphoric acid solution into the container so that the components of the chemical solution in the container are adjustable. 10. Semiconductor nitride layer etching system according to one of claims 1 to 8, characterized by a device ( 15 ) for cooling and discharging a chemical solution, which mainly contains phosphoric acid solution, from a treatment container and a device ( 17 ) for injecting fresh phosphoric acid solution into the container, so that the components of the chemical solution in the container are adjustable. 11. Semiconductor nitride layer etching system according to one of claims 9 or 10, characterized in that the silicon concentration in the chemical solution in a treatment container ( 1 ) is adjustable by injecting fresh phosphoric acid solution containing silicon. 12. Semiconductor nitride layer etching system according to one of claims 9 or 10, characterized by a heat exchanger ( 16 ) for heat transfer between phosphoric acid chemical solution to be conducted and phosphoric acid solution to be injected. 13. Semiconductor nitride layer etching system according to one of claims 1 to 12, characterized by a device ( 26 , 28 ) for measuring the relative density of the chemical solution, so that the relative density of the chemical solution can be adjusted by adding water. 14. Semiconductor nitride layer etching system, characterized by a large number of treatment containers ( 1 a, 1 b) which contain chemical solution which mainly contains phosphoric acid solution and also silicon, so that the silicon concentration in the treatment containers ( 1 a, 1 b ) Recorded chemical solution is adjustable by transferring the chemical solution between the treatment containers. 15. The semiconductor nitride layer etching system according to claim 14, characterized by a control unit ( 21 ) which calculates the silicon concentration in the chemical solution in the treatment containers ( 1 a, 1 b) and controls the transfer of the chemical solution between the treatment containers. 16. Semiconductor nitride layer etching system according to one of claims 1 to 15, characterized in that a treatment container ( 1 ) and a chemical solution contacting area of a chemical solution circulation channel consist of a material from which no silicon is dissolved.